1. Field of the Invention
The present invention relates to a novel sulfurated hydrocarbon material having electrochemical activity, high capacity, and good reversibility, which can be used as an electrode material for the secondary battery. More particularly, it relates to a sulfurated hydrocarbon material, which is prepared by the sulfuration of the olefinic unsaturated hydrocarbon, in the presence of a amine promoter. The sulfurated hydrocarbon material contains from 40 to 88% of sulfur and is represented by the formula (CHxSy)z, wherein: x is a real number in the range of 0.5xe2x89xa6xxe2x89xa61.75; y is a real number in the range of 0.2xe2x89xa6yxe2x89xa63.2; and z is an integer equal to or greater than 5. Also, the present invention provides a secondary battery comprising i) a positive electrode comprising said sulfurated hydrocarbon compound; ii) a polymer electrolyte; and iii) a negative electrode made of alkali metal or alkali metal alloy.
2. Description of Prior Art
Battery has a wide spectrum of applications as a key component of modern portable electronic devices. Especially, secondary battery is essential to the development of hand-carrying devices such as mobile telecommunication tools and notebook computers. A series of development of nickel-cadmium, nickel-metal hydride, and lithium ion types has provided advantages in reducing the size and weight of secondary battery. However, the rapid advancement of electronic technology and widespread use of portable devices have been continuously demanding the next generation battery which has higher energy per unit volume or unit weight than the present battery.
Various sulfur compounds including elemental sulfur, organic disulfide, and organosulfur material have been suggested as an electrode material for secondary battery.
The elemental sulfur electrode utilized a reversible redox reaction between sulfur atom (S) and sulfur anion (S2xe2x88x92), which accounts for 1,675 mAh/g of the theoretical capacity. The Naxe2x80x94S battery comprising i) a positive electrode containing elemental sulfur; ii) a negative electrode consisting of sodium metal; and iii) a solid electrolyte, such as xcex2-alumina has been suggested(R. A. Rizzo, W. L. Towle, and M. L. McClanahan, xe2x80x9cSodium/Sulfur Batteriesxe2x80x9d, in D. Linden Ed. xe2x80x9cHandbook of Batteries and Fuel Cellsxe2x80x9d, pp. 32-1xcx9c32-27, McGraw-Hill, New York, 1984). The Naxe2x80x94S battery shall be operated higher than 300xc2x0 C., where electrode material exists in molten phase, which is required for proper activation of electrode and sufficient ion conductivity. Therefore, said battery has been applied to the module of a large battery rather than the power source of a small electronic device, because it demands extra equipments for maintaining high temperature and ensuring safety.
For solving these drawbacks, U.S. Pat. Nos. 5,686,201 and 5,789,108 suggested the secondary battery comprising i) a positive electrode comprising active-sulfur; ii) a negative electrode using lithium metal; and iii) a polymer electrolyte. Even though said battery containing a positive electrode made of active-sulfur has a high capacity of 500 mAh/g-cathode, the maximum capacity was obtained at 90xc2x0 C. and its efficiency at room temperature or sub-room temperature is limited.
The secondary battery using i) organic disulfide compound as a positive electrode and ii) alkali metal as a negative electrode has been disclosed in U.S. Pat. No. 4,833,048. 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and trithiocyanuric acid (TTCA) are representative examples of organic disulfide compound and have high theoretical capacity of 357 and 454 mAh/g, respectively, even though the organic disulfide compound provides only one electron per sulfur in redox reaction, since sulfur atom is connected to organic moiety. A method improving efficiency of organic disulfide electrode by adding polyaniline was disclosed in U.S. Pat. No. 5,571,292.
When two or more thiol groups present in a molecule of organic disulfide, redox reaction of organic disulfide is accompanied with polymerization/monomerization upon formation and cleavage of Sxe2x80x94S bond. Monomerized dimercapto or dithiolato organic material is soluble in organic slovent present in the composition of electrolyte. Dissolution and consequent diffusion of organic disulfide away from the electrode leads to the decrease in the capacity of electrode and renders organic disulfide electrode material a problematic situation for prolonged use and repeated cycle required for secondary battery. Methods to increasing cycleability by preventing a separation of the monomeric organic disulfide material from the electrode include an addition of copper or silver metal powder to the electrode composition as disclosed in U.S. Pat. No. 5,665,492. And, a method using metal complex of organic disulfide as an electrode material was described in European Pat. 797,264, A2.
An electrode material having high capacity by introducing multi-sulfide bond into organic disulfide material was disclosed in U.S. Pat. No. 5,723,230. A lithium secondary battery using organic sulfide containing heptasulfide has a theoretical capacity more than 4,000 Wh/kg. But, when multi-sulfide bond is involved in electrode reaction, the sulfur-sulfur bond in polymer structure is cleaved upon reduction in the way organic disulfide material undergoes. Problematic diffusive dissolution of monomerized active material takes place and cause the decrease in the cycleability.
Since elemental sulfur has high energy density, efforts to prepare organosulfur material with high sulfur content have been continues. U.S. Pat. No. 4,664,991 suggests a polymeric organosulfur material which was prepared by reacting polyacetylene and sulfur at high temperature. Energy density of a protype cell with the organosulfur polymer was reported to be 1,850 Wh/kg.
Further, polycarbon disulfide (PCS) which is prepared by reductive polymerization of carbon disulfide was disclosed in U.S. Pat. Nos. 5,441,831, 5,460,905, 5,601,947, and 5,690,702. U.S. Pat. No. 5,529,860 suggested polyacetylene-co-polysulfur (PAS) material prepared by the reaction of acetylene with sulfur in the presence of metal amide. The composition of organosulfur compound is represented by the formula (CSm)n where mxe2x89xa72.5 and has theoretical capacity of 700xcx9c1,200 mAh/g. Even though the exact structure of above materials has not been determined, the organosulfur compound was suggested to comprise the structure units shown below. 
The PCS material basically has carbon-carbon bond backbone and does not undergo polymerization/depolymerization upon redox reaction. However, double bonds suggested in the structural unit are chemically vulnerable and provide potential reactive sites upon repeated oxidation and reduction.
Even though many attempts have been made to use sulfur containing compounds as a high-energy electrode material as described above, said sulfur materials needs to be improved to have higher discharge capacity and extended cycle life for its practical use in rechargeable battery.
The object of the present invention is to provide a novel sulfurated hydrocarbon (SHC) material having electrochemical activity, high capacity, and good reversibility which is useful as an electrode material of a secondary battery with high energy density per weight and good cycleability.
The SHC material of the present invention, which is prepared by the sulfuration of unsaturated olefinic hydrocarbon compound in the presence of an amine promotor, contains from 40 to 88% of sulfur and is represented by the formula (CHxSy)z, wherein: x is a real number in the range of 0.5xe2x89xa6xxe2x89xa61.75; y is a real number in the range of 0.2 xe2x89xa6yxe2x89xa63.2; and z is an integer equal to or greater than 5. The SHC material of the present invention has a stable polymeric backbone consisting of carbon-carbon bond which is not altered upon oxidation or reduction
Another object of the present invention is to provide a secondary battery comprising i) a positive electrode comprising said SHC material; ii) a polymer electrolyte; and iii) a negative electrode made of alkali metal or alkali metal alloy.
Accordingly, the present invention provides a rechargeable secondary battery having high capacity at room temperature. Further, the secondary battery of the present invention consists of all solid components and dose not occur any problems relating to the use of liquid electrolyte such as leakage or pressure development, and it can be easily fabricated in a suitable shape according to various application purposes of battery.